It is well known that layered materials, such as phyllosilicates, can be separated or exfoliated into their individual clay platelets, as disclosed in this assignee's U.S. Pat. Nos. 5,552,469; 5,578,672; and 5,698,624. The exfoliated platelets are useful as fillers for polymeric materials to achieve increases in strength, temperature resistance, gas impermeability, and other properties. While the technology has existed for many years for exfoliating clay platelets and combining such clay platelets with polymeric materials, this technology has not been commercialized, for one reason, among others, that while the addition of exfoliated clay platelets to the polymeric materials has substantially enhanced one or more properties of the polymer, the addition of clay impurities together with the exfoliated platelets has caused a marginal improvement, or has actually caused a decrease in properties that the platelets are designed to increase. Thus far, it has been impossible to sufficiently purify a layered material, such as a phyllosilicate, particularly a smectite clay, such that exfoliated platelets obtained from the purified clay are sufficiently free from clay impurities to significantly enhance the desired properties of the polymer.
Prior attempts to purify a layered material, such as a smectite clay, have included the step of analyzing the clay, such as by x-ray fluorescence, to deterine an elemental analysis of the clay, and then analyzing the clay, such as by an x-ray diffraction (XRD) analysis, in order to identify existing crystalline impurities. These impurities, such as feldspar, quartz and the like can be separated from the smectite clay deposit using well-known physical separation techniques, such as one or more hydrocyclones or a centrifuge. It has been found that identification of crystalline impurities by a technique such as x-ray diffraction is insufficient since it has been found that clay deposits, particularly smectite clay deposits, such as sodium montmorillonite and/or calcium montmorillonite, may include a substantial proportion of amorphous impurities, such as amorphous silica, which cannot be identified by x-ray diffraction. Also, it has been found that using existing technology, it is commercially and/or economically extremely difficult to separate any impurity, e.g., amorphous silica or crystalline impurities, if the impurity is present in the clay deposit in a particle size of five microns or less, particularly less than about one micron.
Thus, there exists a need in the art for a method of identifying clay compositions that include crystalline and amorphous impurities, particularly amorphous silica, within the clay compositions. In accordance with the present invention, it has been found that by using a combination of a means to identify the crystalline components of a clay deposit, such as x-ray diffraction and x-ray fluorescence, together with a means for determining amorphous impurities, which requires a knowledge of crystalline chemistry and mineralogy or clay structure, the components of the clay composition can be determined, including the amount and type of amorphous impurities, particularly amorphous silica impurities, such that the composition of a clay deposit can be determined, accurately, prior to purification of the clay.